Add option to log raw server communication

[mk-pmb]

Sorry for having necromanced #1430 first; I didn't remember I had already mentioned it in #1797.
I still chat on FreeNode where multiple encodings are used. While I like the idea of supporting a fallback encoding, it has the major problem that we'd need to know the possible encodings in advance.
Could someone add an option to log raw original server transmissions, so I can try and detect the appropriate encoding retrospectively?
That would help a lot in recovering conversations after they turned out to have been interesting.

[TingPing]

Sounds like a duplicate issue?

[mk-pmb]

I couldn't find another issue about logging the raw transmissions. All that I found were about trying to decode the transmissions in better ways inside hexchat, for varying definitions of "better".
#1430 is about plugins, which might be one way of implementing the logging.